B + B + 3 + B + 4 = 31
Solve for B.
Donna is one year older than her sister, and her sister is 3 years older than their brother. If the sum of their ages is 31, how old is Donna?
2 answers
D = s + 1
s = b + 3 ... b = s - 3
D + s + b = 31
s + 1 + s + s - 3 = 31
find s, then substitute back
s = b + 3 ... b = s - 3
D + s + b = 31
s + 1 + s + s - 3 = 31
find s, then substitute back